;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2013, 2014, 2015, 2016 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (test-monads)
  #:use-module (guix tests)
  #:use-module (guix store)
  #:use-module (guix monads)
  #:use-module (guix grafts)
  #:use-module (guix derivations)
  #:use-module (guix packages)
  #:use-module (gnu packages)
  #:use-module (gnu packages bootstrap)
  #:use-module ((gnu packages base) #:select (coreutils))
  #:use-module (ice-9 match)
  #:use-module (rnrs io ports)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-64))

;; Test the (guix monads) module.

(define %store
  (open-connection-for-tests))

;; Globally disable grafts because they can trigger early builds.
(%graft? #f)

(define %monads
  (list %identity-monad %store-monad %state-monad))

(define %monad-run
  (list identity
        (cut run-with-store %store <>)
        (cut run-with-state <> '())))

(define-syntax-rule (values->list exp)
  (call-with-values (lambda () exp)
    list))


(test-begin "monads")

(test-assert "monad?"
  (and (every monad? %monads)
       (every (compose procedure? monad-bind) %monads)
       (every (compose procedure? monad-return) %monads)))

;; The 3 "monad laws": <http://www.haskell.org/haskellwiki/Monad_laws>.

(test-assert "left identity"
  (every (lambda (monad run)
           (let ((number (random 777)))
             (with-monad monad
               (define (f x)
                 (return (* (1+ number) 2)))

               (= (run (>>= (return number) f))
                  (run (f number))))))
         %monads
         %monad-run))

(test-assert "right identity"
  (every (lambda (monad run)
           (with-monad monad
             (let ((number (return (random 777))))
               (= (run (>>= number return))
                  (run number)))))
         %monads
         %monad-run))

(test-assert "associativity"
  (every (lambda (monad run)
           (with-monad monad
             (define (f x)
               (return (+ 1 x)))
             (define (g x)
               (return (* 2 x)))

             (let ((number (return (random 777))))
               (= (run (>>= (>>= number f) g))
                  (run (>>= number (lambda (x) (>>= (f x) g))))))))
         %monads
         %monad-run))

(test-assert "lift"
  (every (lambda (monad run)
           (let ((f (lift1 1+ monad))
                 (g (apply lift1 1+ (list monad))))
             (with-monad monad
               (let ((number (random 777)))
                 (= (run (>>= (return number) f))